Adding post_tag Taxonomy Support for all WordPress Post-types

posttag-taxonomy-all-post-types.php

<?php

function add_post_tag_support() {
    $post_types = get_post_types();        
    foreach ($post_types as $post_type) {
        register_taxonomy_for_object_type('post_tag', $post_type);
    }
}

add_action( 'init', 'add_post_tag_support', 99 );